International Union for Nature Conservation (IUCN)

Aerial baiting from helicopters with a bait-sowing bucket and GPS to ensure coverage with anticoagulant toxins in cereal-based baits can reliably eradicate rodents on islands. Current best practice for temperate islands is to bait in winter when the rodents are not breeding, rodent numbers are lowest so competition for toxic baits is lowest, natural food is likely to be scarce, and many non-target species are absent from the island. However, short winter day lengths at high latitudes restrict the time helicopters can fly and poor weather in winter may increase risks of failure.

Invasive rodents are present on approximately 80% of the world’s islands and constitute one of the most serious threats to island biodiversity and ecosystem functioning. The eradication of rodents is central to island conservation eff orts and the aerial broadcast of rodenticide bait is the preferred dispersal method. To improve the efficiency of rodent eradication campaigns, the generation of accurate and real-time bait density maps is required.

A pilot project for the eradication of beavers (Castor canadensis) in Tierra del Fuego started as part of a bi-national agreement, signed between Argentina and Chile, to restore the affected environments. The project covers nine pilot areas of different landscapes and land tenures in the Argentinian part of Isla Grande de Tierra del Fuego. We report on the results from operations in the fi rst of the pilot areas.

Aerial broadcast application is currently one of the most common methods for conducting rodent eradications on islands, particularly islands greater than 100 ha or with complex and difficult topography where access by ground teams is difficult. Overall, aerial broadcast applications have a high success rate, but can be burdened by logistical, regulatory, and environmental challenges. This is particularly true for islands where complex shorelines, sheer terrain, and the interface with the marine environment pose additional risks and concerns.

Eradication techniques using ground-based devices were developed in New Zealand in the early 1970s to target invasive rodents. Since then, different bait station designs, monitoring tools and rodenticide baits have been developed, and changes in field techniques have improved and streamlined these operations. The use of these techniques has been taken around the world to eradicate rodents from islands. Eradication technology has moved rapidly from ground-based bait station operations to aerial application of rodenticides.

Invasive rodents have significant negative impacts on island biodiversity. All but the smallest of rodent eradications currently rely on island-wide rodenticide applications. Although significant advances have been made in mitigating unintended impacts, rodent eradication on inhabited islands remains extremely challenging. Current tools restrict eradication efforts to fewer than 15% of islands with critically endangered or endangered species threatened by invasive rodents.

Since 1999, the black rat (Rattus rattus) has been eradicated from 14 Italian islands, and eradication is ongoing on a further five islands. Most projects were funded by the European Union (EU) Life Programme. Over the years, eradication techniques have been improved and adapted to different situations, including aerial bait distribution on islands with large inaccessible areas, which otherwise would have relied on a manual bait distribution.

Sand Island, Midway Atoll National Wildlife Refuge (MANWR), is home to 21% of all nesting black-footed albatross (Phoebastria nigripes) and 47% of all nesting Laysan albatross (P. immutabilis) worldwide. During the 2015–2016 nesting season predation and disturbance by non-native house mice (Mus musculus), here documented for the first time, resulted in 70 abandoned nests, 42 adult birds killed and 480 wounded. In the following nesting season the affected area increased, resulting in 242 dead adults, 1,218 injured birds and 994 abandoned nests.

The Chagos Archipelago comprises some 58 islands covering 5,000 ha in the centre of the Indian Ocean. Black rats (Rattus rattus) were introduced about 230 years ago and have likely had a severe impact on the native terrestrial fauna, which is dominated by seabirds and land crabs. Most of the archipelago’s terrestrial land mass is vegetated with old coconut plantations, with over 75% of the native forest cleared for coconut from 26 of the largest islands.

The world is facing a biodiversity crisis. Nowhere is that more apparent than on oceanic islands where invasive species are a major threat for island biodiversity. Rats are one of the most detrimental of these and have been the target of numerous eradication programmes; a well-established conservation tool for island systems.